1. Field of the Invention
The present invention relates to an injection molding machine in which a screw unit which is provided with a drive is mounted through a carrier on a base frame, wherein the screw unit can be connected to a tool clamping plate in a frictionally engaging manner.
2. Description of the Related Art
An injection molding machine of the above-described type is known, for example, from German Patent No. 32 49 092. This known injection molding machine has an injection unit which includes a screw in a heating cylinder and is supported by a housing provided on the machine bed. An axial forward or rearward movement of the injection unit presses the injection unit against the tool or moves it away from the tool. The injection molding procedure is carried out with different lengths and diameters of the plasticizing cylinders. In the known machine, different lengths of the plasticizing cylinder are compensated by appropriately increasing the displacement stroke. As a result, the machine has the disadvantage that the use is cumbersome when large differences in the lengths of the plasticizing cylinders occur. Moreover, it becomes difficult to mount plasticizing cylinders which exceed scheduled lengths.
In very long plasticizing cylinders, it may be necessary to support the front portion of the screw. An example of this type is known from DE-OS 40 04 478 in which the plasticizing unit is not only supported on the gear housing but also on a fork-type support. The fork-type support and the housing rest on a common base which is moved by a drive on sliding guide means until contact is made with the tool and away from the tool. The concept of the example described in DE-OS 40 04 478 and in German Patent No. 32 45 092 is the same, so that the disadvantages are also the same.
U.S. Pat. No. 3,169,275 discloses an injection molding machine in which the portion of the housing of the plasticizing unit with the outlet opening rests on a carriage-type stand or pedestal and the housing part at the base end is in connection with another stand which can be driven by a motor. The length of the housing of the plasticizing unit can be changed by means of coaxially arranged cylinders, wherein the screw is axially supported during the injection procedure and the plastics material compound is pressed similar to an extruder out of the plasticizing unit by telescoping the plasticizing unit together. For this purpose, in the head part of the plasticizing unit, a frame is formed of the elements crossbeam, head flange and connecting rods, wherein this frame facilitates the length changes by means of hydraulic units. These length changes can be carried out only within narrow limits and are closely linked to the injection operation. The plasticizing unit is pressed against the tool clamping plate essentially through connecting rods by means of drives which are arranged far away from the tool clamping plate.
The injection molding machine known from U.S. Pat. No. 3,169,275 is not capable of using plasticizing units having substantially different diameters mid lengths without reassembly, wherein simple instructional means achieve high accuracy of guidance and the possibility of introducing large drive forces.
The injection molding machine known from the aforementioned U.S. patent does not have a carriage which is engaged over the shortest distance at the front side by a moving unit fastened on the tool clamping plate and is pressed against the tool plate. Morever, the machine does not have elements which facilitate a placement of the housing part with the opening in a positively engaging manner in the front portion of the carriage which would allow a simple change of the acting point of the housing of the plasticizing cylinder which itself has a fixed length.
The machine further does not include means for connecting plasticizing housings of different lengths and different diameters to an undercarriage which is slidable on a base frame.
DE-A-15 54 768 discloses an injection molding machine for plastics materials which can be pivoted about a pivot point and whose front housing part is pressed by a screw connection against an insert of the tool clamping plate.
DE-A 15 54 768 does not disclose a carriage which facilitates in a simple manner a fastening with positive engagement of the housing part with opening. Also, there are no elements which would essentially avoid reassembly of plasticizing units even when the diameters and lengths are substantially different.